Infrared (IR) radiation refers to that part of the electromagnetic spectrum where the wavelength is longer than visible light, but shorter than radio waves, i.e., between approximately 750 nm and 1 mm. Cameras can be used to acquire IR images. Because IR images can capture thermal characteristics of objects, IR images are useful for scenes with extremely low light conditions, such as natural outdoor scenes at night. Infrared imaging can be used in surveillance systems to detect ‘warm’ objects, such as people, animals and vehicles. It should be noted that infrared images can also be acquired of day time scenes.
IR imaging, unlike visible imaging, does not depend on lighting conditions, but rather on varying temperatures. Therefore, IR imaging can operate under very low light conditions, such as the nighttime. Even in the daytime, the independence on lighting conditions can be an advantageous because lighting conditions generally change faster than temperature, especially in scenes where clouds temporarily occluding sunlight, or as objects move in and out of shadows.
Therefore, background adaptation is generally less crucial in IR images than in visible images. Foreground detection using background subtraction is also easier with IR images because there are no shadows, while shadow removal is an important issue for background subtraction with visible images.
However, due to camera technology limitations, uncooled IR cameras tend to have a lower spatial resolution and are less sensitivity than color cameras. This can limit an efficacy of a classification step based on object silhouette or shape, especially when the object is far from the cameras.